Method for determining the instantaneous temperature of a medium

ABSTRACT

A method for determining the instantaneous temperature of a medium, the medium surrounding an element able to be electrically heated at least intermittently to a constant, known temperature. It is provided for the instantaneous temperature of the medium to be determined from a heating power supplied to the element.

The present invention relates to a method for determining the instantaneous temperature of a medium having the features recited in the definition of the species in claim 1.

BACKGROUND INFORMATION

It is known that an ambient temperature, e.g. of a unit of a motor vehicle, is an important auxiliary quantity for a number of control, regulating, and monitoring operations. To process this auxiliary quantity, measuring systems are known via which an instantaneous ambient temperature is able to be measured. For this purpose, temperature sensors are known that, for example, supply a signal proportional to the actual temperature on the basis of temperature-dependent resistances.

It is also known to use gas sensors via which a gas composition of a medium, e.g. of the ambient air, is able to be measured. These gas sensors function, for example, according to the principle of variable resistances, e.g. on a metallic oxide basis, and need an operating temperature for this purpose. Therefore, it is known, to assign the gas sensors a heating element via which the gas sensors are able to be heated to the needed operating temperature.

Such gas sensors are used, for example, in air conditioning systems. In order to be able to perform a temperature measurement at the same time as the gas analysis, it is known to use a combined sensor element that includes the gas sensor as well as a temperature measurement sensor. In this context, it is disadvantageous that this system of two sensors based on different operating principles necessitates complicated adaptive work with regard to the set-up, control, and the like.

SUMMARY OF THE INVENTION

In contrast, the method of the present invention having the features recited in claim 1 provides the advantage that an instantaneous temperature is able to be measured in a simple manner. As a result of an element able to be heated at least intermittently to a constant, known temperature being used such that the instantaneous temperature of the medium surrounding the element is determined from a heating power supplied to the element, it is advantageously possible to dispense with the mounting of an additional temperature measurement sensor. Thus, the design of such sensor elements is significantly simplified. In addition to the material savings connected with this and a reduction in manufacturing costs, such sensor have a simpler design, so that they are able to be used in diverse applications without a significant need for adaptation.

In a preferred refinement of the present invention, it is provided that the heating power used to determine the instantaneous temperature is ascertained from a measured heating voltage and a measured heating current. Therefore, an operating parameter that is proportional to the ambient temperature is provided in a simple manner on the basis of known relationships according to which the heating power is the product of the heating voltage and the heating current. Using algorithms preferably able to be processed by microprocessors, the heating power to be introduced to reach the necessary, known, constant operating temperature of the heating element is evaluated as a measure of the instantaneous temperature of the medium on the basis of a known initial temperature of the sensor recording the heating power and of known geometry constants, e.g. in particular the heat transfer resistance to the medium. In a particularly preferred refinement of the present invention, the relationship of heating power to ambient temperature is able to be stored in a table in a storage means assigned to the microprocessor, so that when measuring a certain heating power, it is able to be immediately assigned to the instantaneous temperature of the medium given for it.

In an additional preferred refinement of the present invention, it is provided for the heating power to be determined from a pulse duty factor of a closing frequency of the heating voltage. It is known per se to switch on the heating voltage in a timed manner in order to reach a constant heating temperature, so that the resulting pulse duty factor provides a quantity proportional to the supplied heating power. This pulse duty factor of the heating voltage is known for regulating the temperature of the heating element and is consequently able to be tapped off in a simple manner and used for determining the instantaneous temperature of the medium.

In a further preferred refinement of the present invention, it is provided for the heating power to be determined from a time span that occurs between a switching-off time of a heating voltage and a re-closing time of the heating voltage during a two-step control. It is known per se to set a certain heating temperature in that the limiting temperature values being exceeded or not met is measured via a two-step control, and the heating voltage is switched off when the values are exceeded and switched on when they are not met. As a result, a heating temperature in the range defined by the limiting temperature values is maintained. The resulting time span between the switching-off of the heating voltage and the switching back on of the heating voltage is a signal that is proportional to the supplied heating power for maintaining the heating temperature and that is evaluated in a simple manner and may be used as a measure for the instantaneous temperature of the medium.

It is clear that measured quantities proportional to the heating power are tapped off in a simple manner using the method of the present invention, and a signal proportional to the instantaneous temperature of the surrounding medium is able to be determined from this on the basis of known constants of the system. The design approach is able to be implemented in a simple manner in existing control units or the like, so that an additional expenditure for structural elements is not necessary.

Further preferred embodiments of the present invention follow from the remaining features specified in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention is explained in greater detail in the light of exemplary embodiments with reference to the appertaining drawings. The figures show:

FIG. 1 a circuit configuration for determining an instantaneous temperature in a first variant of an embodiment;

FIG. 2 a circuit configuration for determining an instantaneous temperature in a second variant of an embodiment;

FIG. 3 a signal pattern of a heating voltage;

FIG. 4 a temperature progression of a known heating temperature; and

FIG. 5 a curve of a heating voltage resulting from the temperature progression according to FIG. 4.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The exemplary embodiments explained below start out from a gas sensor element 10 to which an internal heating device 12 is assigned for reaching an operating temperature of gas sensor element 10. Heating device 12 is formed by an electrical heating resistor RH. The design and operating mode of such gas sensor elements 10 are generally known, so that this is not described in greater detail within the framework of the present description.

Gas sensor element 10 is assigned to a medium 14, e.g. the air in an interior space of a motor vehicle, the interior space of a building, or any general measuring point. This medium 14 has an instantaneous ambient temperature T_(U). In the following explanation of the exemplary embodiments, it is assumed that a measuring signal corresponding to instantaneous ambient temperature T_(U) is to be determined and to be used as an auxiliary quantity for additional control, regulating, or monitoring functions.

Gas sensor element 10 has a known design and is configured such that its gas-sensitive regions are optimally coupled to medium 14. This results in a known thermal transfer resistance R_(TH) between gas sensor element 10 and medium 14. Heating element 12 is assigned to the gas-sensitive regions of gas sensor element 10, so that a minimal as possible heating power P_(H) is needed to be able to bring gas sensor element 10 to the necessary operating temperature of, e.g. greater than 300° C. To achieve this, a thermal capacitance of gas sensor element 10 is as low as possible, and a thermal leakage resistance of gas sensor element 10 is as great as possible. As a result, it is possible to quickly reach the necessary operating temperature while the dissipation heat of gas sensor element 10 emitted into the surrounding medium is low.

These initial considerations result in heating power P_(H) supplied to gas sensor element 10 being viewed in direct connection with ambient temperature T_(U) of medium 14. On the basis of the known geometry of gas sensor element 10, its thermal capacitance, its thermal leakage resistance, and the thermal transfer resistance to medium 14 are known and may be used as constants when determining ambient temperature T_(U).

Assigned to gas sensor element 10 is a temperature sensor 16 via which an actual temperature T_(actual) of gas sensor element 10 is measured. This actual temperature T_(actual) is provided to a heating controller 18. Heating controller 18 compares temperature T_(actual) to a temperature T_(setpoint) for gas sensor element 10 and supplies a control signal S, with which a voltage source 20 is controllable, as a function of a difference T_(setpoint)−T_(actual). A level of supply voltage U_(V) for heating element 12 of gas sensor element 10 is controlled via control signal S. Heating voltage U_(H) and heating current I_(H), which flows over a measuring resistor R_(M), are able to be continuously determined from this instantaneous supply voltage U_(V) via measuring means not shown in detail. Instantaneous heating power P_(H) is able to be determined on the basis of the known relationship heating power P_(H)=heating voltage U_(H)·heating current I_(H). As described above, this instantaneous heating power P_(H) is a function of instantaneous temperature T_(U). Using a control unit 22 indicated here, which obtains instantaneous heating power P_(H), setpoint temperature T_(S) of gas sensor element 10, and thermal transfer resistance R_(TH) between gas sensor element 10 and medium 14 as input quantities, a control signal S_(TU) corresponding to instantaneous ambient temperature T_(U) of medium 14 is made available on the basis of the relationship T_(U)=T_(setpoint)−R_(TH)·P_(H).

The consideration of temperature T_(setpoint) of gas sensor element 10 assumes that via heating controller 18, actual temperature T_(actual) of gas sensor element 10 essentially corresponds to setpoint temperature T_(setpoint).

FIG. 2 explains a second variant of an embodiment for determining instantaneous ambient temperature T_(U) of medium 14. Parts that are the same as in FIG. 1 are provided with identical reference numerals and are not explained again. According to the circuit configuration known per se and shown in FIG. 2, supply voltage source 20 is operated by a constant supply voltage U_(V). Heating voltage U_(H) for keeping gas sensor element 10 at setpoint temperature T_(setpoint) is regulated by controlling a circuit element 24 in a clocked manner via heating controller 18. As FIG. 3 shows, as a result of a pulse duty factor of heating controller 18 heating voltage U_(H) is applied for a heating duration t_(H). While this heating voltage U_(H) is being applied, heating element 12 heats up until temperature sensor 16 signals that temperature T_(setpoint) has been reached. Depending on whether ambient temperature T_(U) of medium 14 decreases or increases, a more or less large heating power P_(H) of heating element 12 is necessary for gas sensor element 10 to be able to be adjusted to its known constant operating temperature. This heating power results from the pulse duty factor of heating time t_(H) to a total heating period T. This heating regulation is known per se. A resulting pulse duty factor $\frac{t_{H}}{T}$ is consequently directly dependent on ambient temperature T_(U). The pulse duty factor $\frac{t_{H}}{T}$ is tapped off and supplied to control unit 22. Supply voltage U_(V), heating resistance R_(H), setpoint temperature T_(setpoint), and thermal transfer resistance R_(TH) are available to control unit 22 as additional known constant input quantities.

On the basis of the relationship $T_{U} = {T_{S} - {R_{TH} \cdot \frac{U^{2}}{R_{H}} \cdot \frac{t_{H}}{T}}}$ a control signal S_(TU), which is directly proportional to instantaneous ambient temperature T_(U), is able to be provided on the basis of the known quantities and instantaneous pulse duty factors $\frac{t_{H}}{T}.$ .

The circuit configuration according to FIG. 2 is able to be operated in a manner known per se via a so-called two-step control. In this context, sensor temperature T_(S) is controlled between a top limiting value T_(GO) and a bottom limiting value T_(GU) via heating controller 18 by controlling heating voltage U_(H). Temperature T_(actual) is determined via temperature sensor 16 and supplied to heating controller 18. The heating controller compares temperature T_(actual) with top limiting value T_(GO) and with bottom limiting value T_(GU), respectively. If temperature T_(actual) reaches top limiting value T_(GO) circuit element 24 is switched off by heating controller 18, while when bottom limiting value T_(GU) is reached by actual temperature T_(actual), circuit element 24 is switched on. This results in the characteristic curve of sensor temperature T_(S) shown in FIG. 4. Defining top limiting value T_(GO) and bottom limiting value T_(GU) results in a temperature hysteresis Δ T of heating element 12. This results in the switching-off times t_(off) of circuit element 46 shown in FIG. 5 and corresponding switching-on times t_(on) of circuit element 24. According to this, heating voltage U_(H) is also clocked as a function of the characteristic curve of temperature hysteresis Δ T. For time t_(off) the following relationship applies $t_{off} = {{- \tau} \cdot {l_{n}\left( {1 - \frac{\Delta\; T}{T_{GO} - T_{U}}} \right)}}$ where τ is a thermal time constant of gas sensor element 10. On the basis of known time constant τ and known temperature hysteresis ΔT as well as known top limiting temperature T_(GO), switching-off time T_(off) is directly dependent on instantaneous ambient temperature T_(U) of medium 14. A signal S_(TU) corresponding to ambient temperature T_(U) is consequently able to be provided via control unit 22.

It becomes clear that a necessary heating power P_(H) or heating voltage U_(H) is able to be directly used for determining ambient temperature T_(U) via simple method steps from measured values or constants known per se of a gas sensor element 10.

Of course, the present invention is not restricted to the represented exemplary embodiment. Thus, it is presupposed in the description of the exemplary embodiment that gas sensor element 10 is operated at a heating temperature that is constant over time. This heating temperature may also be variable with respect to time. Taking temperature T_(setpoint) or then changed top limiting value T_(GO) into consideration also makes it possible to reach a setpoint temperature that is variable over time when determining instantaneous ambient temperature T_(U) in a simple manner. Moreover, the use of the method of the present invention for determining ambient temperature T_(U) is not limited to gas sensor elements. It is crucial for an element, e.g., a voltage reference, a time/frequency standard, or the like, able to be heated at least intermittently to a constant, known temperature to be present. The heating power to be supplied in order to reach the at least intermittently constant, known temperature is then used as an output variable for determining instantaneous ambient temperature T_(U). 

1. A method for determining an instantaneous temperature of a medium, comprising: regulating a temperature of an element surrounded by the medium to a constant, known temperature by electrically heating the element, at least intermittently; determining the heating power from a pulse duty factor of a closing frequency of the heating voltage; and determining the instantaneous temperature of the medium from a heating power supplied to the element, the heating power being adjusted as a function of one of: i) a difference between an actual temperature of the element and a setpoint temperature of the element, and ii) a difference between the actual temperature of the element and a limiting value of the temperature, the limiting value being one of a top and bottom limiting value of the temperature.
 2. The method as recited in claim 1, further comprising: determining the heating power from a measured heating voltage and a measured heating current.
 3. A method for determining an instantaneous temperature of a medium, comprising: regulating a temperature of an element surrounded by the medium to a constant, known temperature by electrically heating the element, at least intermittently; determining the instantaneous temperature of the medium from a heating power supplied to the element, the heating power being adjusted as a function of one of: i) a difference between an actual temperature of the element and a setpoint temperature of the element, and ii) a difference between the actual temperature of the element and a limiting value of the temperature, the limiting value being one of a top and bottom limiting value of the temperature; and determining the heating power from a time span between a switching-off time of the heating voltage and a re-closing time of the heating voltage during a two-step control of a temperature of the element.
 4. The method as recited in claim 2, further comprising: comparing the determined heating power to known constant parameters of the element; and providing a signal proportional to the instantaneous temperature based on the comparison.
 5. The method as recited in claim 4, wherein at least one of a setpoint temperature of the element, thermal transfer resistance to the medium, supply voltage, and heating resistance is used as constants of the element.
 6. The method as recited in claim 1, further comprising: changing the constant, known temperature.
 7. A method for determining an instantaneous temperature of a medium, comprising: regulating a temperature of an element surrounded by the medium to a constant, known temperature by electrically heating the element, at least intermittently; determining the instantaneous temperature of the medium from a heating power supplied to the element, the heating power being adjusted as a function of one of: i) a difference between an actual temperature of the element and a setpoint temperature of the element, and ii) a difference between the actual temperature of the element and a limiting value of the temperature, the limiting value being one of a top and bottom limiting value of the temperature; and generating a control signal corresponding to the instantaneous temperature of the medium, the control signal being generated as a function of the setpoint temperature of the element minus the product of a heating power supplied to the element and a thermal transfer resistance between a gas sensor element and the medium.
 8. A method for determining an instantaneous temperature of a medium, comprising: regulating a temperature of an element surrounded by the medium to a constant, known temperature by electrically heating the element, at least intermittently; determining the instantaneous temperature of the medium from a heating power supplied to the element, the heating power being adjusted as a function of one of: i) a difference between an actual temperature of the element and a setpoint temperature of the element, and ii) a difference between the actual temperature of the element and a limiting value of the temperature, the limiting value being one of a top and bottom limiting value of the temperature; and generating a control signal corresponding to the instantaneous temperature of the medium, the control signal being generated as a function of the setpoint temperature of the element minus the product of a pulse duty factor of a closing frequency of the heating voltage, a thermal transfer resistance between a gas sensor element and the medium, and a heating voltage squared divided by a heating resistance. 